The present invention relates to a method of improving the adhesion resistance of a silver halide light-sensitive medium for use in printing (hereinafter referred to as a "light-sensitive printing medium"). More particularly, it relates to a method of improving the adhesion resistance of a light-sensitive printing medium, which further improves the color-retention properties of a backing layer after development processing.
A light-sensitive printing medium generally comprises a plastic support, such as cellulose acetate and polyester films, a silver halide emulsion layer and a surface protective layer which are provided on one side of the support, and a backing layer composed of gelatin as a binder and dye, which is provided on the other side of the support.
Hydrophilic colloid layers composed mainly of gelatin, such as the foregoing surface protective layer and backing layer, have the disadvantage that they are greatly influenced by humidity and temperature; that is, they stretch and contract according to changes in humidity and temperature. This leads to reduction in the dimensional stability of a photographic light-sensitive medium. The poor dimensional stability of the photographic light-sensitive medium is a serious problem for the light-sensitive printing medium.
In order to provide photographic light-sensitive media having excellent dimensional stability, a method of softening the binder has been proposed. For example, a method of incorporating a polymer latex into the binder is known, as described in Japanese Patent Publication Nos. 4272/64, 17702/64 and 13482/68 and U.S. Pat. Nos. 2,376,005, 2,763,625, 2,772,166, 2,852,386, 2,853,457, 3,397,988, 3,411,911, 3,411,912 and 3,525,620.
Hydrophilic colloid layers composed of a binder containing therein a polymer latex, however, are increased in adhesive properties or sticking properties at high humidities, particularly in a high temperature and high humidity atmosphere. That is, when they come in contact with other members, they easily stick thereto. This phenomenon occurs between photographic light-sensitive media themselves or between the photographic light-sensitive medium and another member to come into contact therewith during the course of production, processing or storage of photographic light-sensitive media, and often creates various problems.
A method of preventing the easy bonding of the hydrophilic colloid layer (which is called in the art a method of improving the adhesion resistance of the hydrophilic colloid layer; therefore, the term "adhesion resistance" is used in the specification to mean an ability to resist such bonding) includes a so-called matting technique. This technique increases the coarseness of the surface of the colloid layer by incorporating thereinto fine particles of, for example, silica, magnesium oxide or polymethyl methacrylate having an average grain size of about 1 to 5 microns (hereinafter referred to as a "matting agent").
However, this matting technique has disadvantages. When the matting agent is incorporated into the colloid layer in an amount which provides sufficient adhesion resistance, the transparency of an image formed by development processing of the photographic light-sensitive medium is reduced. Furthermore, the granularity of the image is deteriorated, the sliding properties of the surface of the photographic light-sensitive medium are deteriorated, and the surface of the photographic light-sensitive medium is easily scratched.
A dye is incorporated into the backing layer of the light-sensitive printing medium in order to prevent halation and facilitate the distinction between both sides of the medium. The dye incorporated into the backing layer must be completely removed by development processing. With regard to the color-retention properties, it is said in the art that when the decolorization is insufficient, the color retention properties are poor. However, when decolorization is completely achieved, the color retention-properties are excellent. Accordingly, the term "excellent color retention-properties" is used in the specification to indicate that decolorization after development processing is performed completely.
The poor color-retention properties of the backing layer not only deteriorate the quality of the image after development processing, but also undesirably lengthen the exposure time required for printing the image formed on the light-sensitive printing medium to a printing plate.